Sulfur compounds are a chemically very reactive group of substances, which are widely encountered in biological systems and industrial processes. Currently, considerable effort is being devoted to compounds involving coordination of sulfur-containing molecules to transition-metal ions, e.g., iron, copper and cobalt. In living systems many processes are known in which metal ions play a key role. A better understanding of these processes has resulted from application of basic theory and practices, including, recently, contributions from workers with expertise in the area of transition-metal chemistry. Sulfur compounds are important in a number of systems. Of particular interest in this project are the sulfur amino acids, cysteine and methionine, and related species and the reaction characteristics of metal complexes containing them. The thiols cysteine and cysteamine are enzymatically oxidized to the oxygenated, sulfinic acid form, an important step in the overall metabolism of these compounds. It appears that a transition metal is an essential component in these reactions. The goals of the study are (1) to explore the reactions of cysteine and related thiols and thioethers, bound in metal complexes, with hydrogen peroxide, molecular oxygen, and other oxidizing agents and (2) to use the results obtained to formulate and test models that will lead to an increased understanding of biological thiol oxidations. Primary efforts, including synthetic, physical characterization, and reaction mechanism studies, will be devoted first to cobalt(III) and then to iron complexes.